Preparation of pentachlorocyclopentenone



Pia-ma has, 1950 PENTENONE Earl T. ltfcBee and Jack 8. Newcomer, WestLafayette, Ind., assignorl to.

Purdue Research I Foundation, Lafayette, Ind. a corporation of IndianaNo Drawing. Application June as, 1947,

Serial No. 757,949

1 11 Claims.

The present invention relates to a novel process for the preparation of2,3,4,4,5-pentachloro- 2-cyclopentenone, having the molecular formula:

vide a novel process for the production of 2,3,4.4,5-

2,3,4,4,5-pentachloro-2-cyclopentenone of high purity obtained inexcellent yields directly from hexachlorocyclopentadiene.

The invention essentially comprises heating together, at a tem- Thesulfuric acid employed in the'method of. the'present invention has aconcentration or-' dinarily greater than about per cent, and usually ofa concentration in excess of of 80 per cent.

The reaction time is considerably reduced by em- 'lo'yment of was:higher concentration. When acids of concentration less than 50 per centare used. the reaction rate is ordinarily too-low to be 'flie' reactiontemperatureis a very important and critical factor in performing thepresent invention. Temperatures below about 60 degrees centigrade arenotgenerally productive of a satisfactory reaction rate, while, attemperatures above about 95 degrees centigrade, excessive quantitles ofundesirable byproducts, in some instances including even tars, areformed. However, temperatures of 60 to 95 degrees centigrade aresatisfactory, with temperatures between about '75 to 90 degreescentigrade being especially preferred due to the high yields of desiredproduct obtainable by operating within the said range.

For optimum results, the hydrolysis should be continued until themixture of reaction products exists as a single phase. As introducedinto the reaction zone, the hexachlorocyclopentadiene and sulfuric acidare immiscible and resolve into two layers. Upon agitation of themixture during the reaction period, which is desirable to ensure asatisfactory contact of the reactants, the two layers gradually resolveinto a single layer or phase. Conversions and yields as high as per centmay be obtained by discontinuing the reaction as soon as only asinglephase is present, and purity of the crude product is'highest at thispoint. However, good conversions are obtainable by allowing the reactionto proceed for longer periods of time.

The time required for the reaction is usually between about six andtwelve hours. depending upon concentration of the acid. efficiency ofagitation, and the temperature employed. It desired, a suitableemulsifying agent may be employed to cause more eflicient contact of the.reactants. The mole ratio of acid to hexachlorocyclopentadiene is notcritical, but may be conveniently maintained between about '1- to 1 and6 to l. 1

The objectives of the present invention are most readily accomplishedonly when efllcient-contact of the reactants is provided. Withoutstirring or other agitation, the high yields and purity of the desired2,3.4,4,5-pentachloro 2 a cyclopentenone can not ordinarily be realized.This agitationmay vtake any desired form, such as stirring, s haking,'et cetera, but is considered requisite in the preferred manner ofconducting the reaction.

a mixture of 200 grains of hexachlorocyclopentadienacsciaandeoogramsoftecnni concentrated sulfuric acid(93 per cent) was vigorously agitated for 8 hours at a temperature of 80to 90 degrees centigrade. The solid product with room-temperatureliquid-phase bromination to5-bromo-2,3,4,4,5-pentachloro-2-cyclopentenone, a yellow oil having amelting point of about 3 to 4 degrees centigrade, and thence to 5-bromo-2,3,4,5-tetrachloropentadienoic acid, a white solid having a meltingpoint of 118 to 119 degrees centigrade, by treatment with alkali (KOH)and subsequent acidification (HCl) The .same monobromo acid was obtainedby brominating tetrachloro-5,5-dimethoxycyclopentadiene (the structureof which was established by hydrolysis with concentrated sulfuric acidto form the reactive tetrachlorocyclopentadienone, which immediatelydimerized with the production of octachloro 3a,4,'l.7a tetrahydro 4,7methanoindene-1,8-dione, a known compound) at room temperature in theliquid phase, treating the resulting product with concentrated sulfuricacid to form a dibromotetrachlorocyclopentenone (a white solid whichliberates a gas at its melting point of about 156 degrees centigrade),treating this ketone with alkali, and subsequently acidifying. The acidproduced in this manner has the bromine atom fixed on the terminalcarbon atom. As the acid produced in both cases is the same, theposition of the bromine atom is fixed in 5 bromo 2,3,4,4,5 pentachloro 2cyclopentenone, and thus also the position of the hydrogen in2,3,4,4,5-pentachloro-2-cyclopentenone.

The 2,3,4,4,5 pentachloro 2 cyclopentenone prepared as above did notdepress the melting point of the compound prepared as directed by Zinckeand Meyer, Ann. 367, 7 (1909), and had a calculated chlorine per cent of69.7, found 69.6; M. W. calcd. 254, M. W. found 257.

Example 2 The procedure of Example 1 was repeated, using instead 814grams of hexachlorocyclopentadiene and 1600 grams of concentratedsulfuric acid (93 per cent). A 78 per cent yield of the desired2,3,4,4,5-pentachloro-2-cyclopentenone was obtained also in thisinstance.

The compound 2,3,4,4,5-pentachloro-2-cycicpentenone may be brominated inthe liquid phase at or about room temperature to 5-bromo-2,3,4,4,5-pentachloro-2-cyclopentenone, a compound of the formula:

which may then be dehydrochlorinated with a base, e. g., K03, andsubsequently acidified to produce the compound-bromc-2,3,4,5-tetrachloropentadienoic acid, having the formulaBrC1c=cCl-CCl=CCiCOO The ketone, 2,3,4,4,5-pentachloro-2-cyclopentenone,is considerably more soluble in non-polar organic solvents thanimpurities which are obtained in appreciable quantities when thereaction is conducted at higher temperatures, and may conveniently beseparated from the said impurities by extraction of the product, usuallyin the sulfuric acid solution thereof, with such a non-polar solvent, e.g., chloroform. carbon tetrachloride, or petroleum ether (-100 degreescentigrade).

. Various modifications may be made in the invention without departingfrom the spirit or scope thereof, and it is to be understood that welimit ourselves only as defined in the appended claims.

We claim:

1. The process which includes: heating together, at a temperaturebetween about and 95 degrees centigrade, hexachlorocyclopentadiene andconcentrated sulfuric acid of less than 100 percent concentration, toconvert said hexachlorocyclopentadiene to 2,3,4,4,5-pentachloro-2-cyclopentenone.

2. The process of claim 1, wherein the reaction mixture is agitated.

3. The process of claim 1, wherein the temperature is maintained betweenabout and degrees centisra e.

4. The process of claim 1, wherein 2,3,4,4,5-pentachloro-z-cyclopentenone is separated from the reaction product.

5. The process of claim 1, wherein the mole ratio of sulfuric acid tohexachlorocyclopentadiene is between about 1 to 1 and 6 to l.

6. The process which includes: heating together, at a temperaturebetween about 60 and degrees centrigrade, hexachlorocyclopentadiene andconcentrated sulfuric acid of less than percent concentration untilattainment of a single phase.

'1. The process which includes: heating together, with agitation, at atemperature between about 60 and 95 degrees centigrade,hexachlorocyclopentadiene and sulfuric acid of at least about 80 andless than 100 per cent concentration, until attainment of a singlephase, and then discontinuing the reaction and separatingpentachlorocyclopenienone from the reaction product.

8. The process which includes: heating together, with agitation, at atemperature between about 75 and 90 degrees centigrade,hexachlorocyclopentadiene and sulfuric acid of at least about 80 andless than 100 per cent concentration,

until attainment of a single phase, and separating the reaction product.

9. The process which includes: heating together, with agitation, at atemperature above about 90 degrees centigrade, hexachlorccyclopentadieneand sulfuric acid of at least about 80 and less than 100 per centconcentration, until the attainment of a single phase, and untilconversion of at least about 50 percent of the hexachlorocyclopentadieneto 2,3,4,4,5-pentachloro- 2- 15 tially immediately upon attainmentthereof.

I 11. The method of claim 10, wherdn fill Um STATE PATINTB2.8.4,,5-penhchloro-2-cyclopentenone ll ex- 4 tracted from the mum: acidsolution with I m g n n-9011! manic aolven mm. T, Balhrd May 26, 104:

OTHER REFERENCES JACK S. NIWCODIIR.

' zincke et $1.. Amman. 387, Dale: 1-13 REFERENCES 01'!!!) um).Thefollowinzreterencesareotrecordin-the file of this patent:

1. THE PROCESS WHICH INCLUDES: HEATING TOGETHER, AT A TEMPERATUREBETWEEN ABOUT 60 AND 95 DEGREES CENTIGRADE, HEXACHLOROCYCLOPENTADIENEAND CONCENTRATED SULFURIC ACID OF LESS THAN 100 PERCENT CONCENTRATION,TO CONVERT SAID HEXACHLOROCYCLOPENTADIENE TO2,3,4,4,5-PENTACHLORO-2CYCLOPENTENONE.